Studies - Lisbon General Drainage Plan - Hydraulic studies in physical model of the Monsanto-Sta. Apolónia tunnel entrance works

The Lisbon City Council developed the Lisbon General Drainage Plan (PGDL) with the main objective of reducing the impact of urban floods in the city. The plan involves the construction of two deep tunnels (diameter of 5.5 m) that will intercept the water collected from the surface - Monsanto-Sta. Apolónia (4,4 km) e Chelas-Beato (1,1 km) – and convey it directly into the Tagus River.

Concerning the project for the drainage tunnels of the city of Lisbon, LNEC carried out a physical model hydraulic study of the entrance works that will be built in Monsanto/Campolide for diverting the pluvial flows from the existing Alcântara tunnel into to the future Monsanto-Sta. Apolónia. The entrance works were conceived to integrate an anti-pollution basin allowing for most rainfall events a pre-treatment of the unitary flood flows prior to the discharge into the Tagus River. As the operating modes and flow ranges involved for this project work are complex and involve unconventional hydraulic structures, the simulation of the main hydraulic operating scenarios on a reduced model, at scale 1:30, was an important tool to validate the project solution.

The scale model was made by means of digital design and fabrication (3D Cad, 3D printing and CNC machining) considering a light and modular design. Comparing with the traditional methods of model construction, this option, innovative at LNEC, made it possible to speed up the construction, improve the geometrical accuracy and simplify the introduction of alternative geometries.

The physical model showed that, in general, the hydraulic operation is adequate for the entire range of flood flow operation foreseen in the project. In addition, it also allowed the identification of various details that can be improved in the final design of the work.